The present invention relates, generally, to systems, processes and devices which use frequency synthesizers and filters and, in particular embodiments, to processes, systems and devices in which the architecture of frequency synthesizing and filtering stages of communication transceivers is improved.
Portable electronic devices have become part of many aspects of personal, business, and recreational activities and tasks. As the popularity of various personal communication devices, such as portable phones, portable televisions and personal pagers increases, the demand for smaller, lighter, more powerful, and more power efficient electronics, which comprises these devices, has also continued to increase.
The demand for smaller, lighter, more powerful, and more power efficient electronics provides motivation for ever increasing levels of circuit integration, in order to minimize the number of integrated circuits and improve the functioning of circuits which compose such systems. As the levels of integration increase and the actual number of integrated circuits within a system decrease, each integrated circuit may need to perform an increased portion of the functions of the overall system. Accordingly, the integration level of integrated circuits continues to increase as the number of integrated circuits within such systems continues to shrink. As more functions are integrated into fewer and fewer integrated circuit packages the number of pins on integrated circuits, i.e. input and output connections, has risen. As the levels of integration, of integrated circuits, increase, circuit packaging and input output pin count become critical design considerations.
Integrated circuits for communication systems must also be concerned with interoperability, that is integrated circuits from one manufacturer must be able to work with a variety of other manufacturers"" integrated circuits. The more integrated circuits that a manufacturer""s product is compatible with the more integrated circuits that that manufacturer may sell. Because of the desire for interoperability, various manufacturers often develop similar interfaces between different integrated circuits. The need for common interfaces is increasingly important as higher density integrated circuits integrate more functions. As more functions are integrated, there is a need for more input output connections to connect the ever-increasing number of functions, within an integrated circuit, to the outside world. To meet the increasing input/output needs of increasingly complex integrated circuits, manufacturers have turned to multiplexed input and output pins, serial and parallel busses to convey information between parts.
Some of the buses, such as the serial I2C bus, are standardized and well defined. Others may adopt similar physical connections, so that the interconnections between parts become de facto standards and only the data communicated is changed, depending on which manufacturer""s devices are being used. One such de facto standard is the serial bus used by the baseband electronics in communications circuits to communicate with the synthesizer portion of the circuitry. The baseband portion of the communications system circuitry is a portion of the circuitry that is used for controlling the system. It commonly includes logic circuitry to control other subsystems, and may control the receiving and processing of commands from the user of the system as well as displays. The synthesizer portion of the circuitry is the portion that commonly controls the synthesis of frequencies for modulating and demodulating signals. Examples of frequency synthesizers controlled by serial busses are the MB15E07SL integrated circuit produced by Fujitsu, the LMX2326 produced by National Semiconductor, and the MC145202 produced by Motorola.
Commonly included with a baseband electronics section and a synthesizer electronics section is a filtering section. A filtering section is typically separate from a synthesizer portion of the circuitry and contains discrete filtering elements. If only one transmit band and one receive frequency band is used, within a communications unit, the associated bandpass filters used with those frequency bands may be hardwired into the circuit, as they would never need to be changed. More and more modern communications devices, however, are required to operate in several communications bands and have the ability to be switched between the bands. An example of a communication system being required to support more than one band is the Japanese Personal Digital Cellular System (PDC). An additional allocation of bandwidth for the Japanese Personal Digital Cellular (PDC) system has required handset radios to support communication channels in three separate receive and transmit frequency bands. Existing SAW (Surface Acoustic Wave) filters, such as the PDC800 produced by Fujitsu, which are commonly used in such applications, can be only used to support one or two of the bands at a time. Because the SAW filters can be used to support only one or two of the bands at a time methods for selecting correct filters for a given communication channel need to be devised.
It is common practice to have an embedded processor control such subsystems. The straightforward approach to solving the filter/band selection problem is to add, to the embedded processor subsystem, digital logic and control signals to switch bandpass filters. The control signals needed may be supplied to circuitry external to the embedded processor subsystem. Embodiments of the present disclosure dispense with the straightforward solution of adding digital logic and control signals to the embedded processor subsystem.
Accordingly, preferred embodiments of the present invention are directed to frequency synthesis and filter selection circuitry, and systems employing the same. Embodiments described herein relate to methods and apparatus for improving control over the selection of bandpass filters, in systems where more than one filter is present. External circuitry can then direct signals through the appropriate filters. Embodiments of the present invention instead use the data which is used to program the frequency synthesizer circuits to control filter selection. By decoding the data from the signals used to program the frequency synthesizer, logic circuitry can determine which frequency is being synthesized, and hence which filter is required. By decoding the data used to program the frequency synthesizer and using it to control the selection of filters the need for additional logic and control signals to select filters can thereby be eliminated.
The elimination of additional control signals to select filters, results in a reduction of the number of connections between the filter selection circuits and the embedded processor subsystem. This reduction saves space, makes for easier circuit board layout, and reduces test time of the baseband processor Integrated Circuit by reducing the amount of I/O pins which must be tested. In addition, designs are simpler because software, logic circuits and other circuitry, which might have been required to drive the additional control circuits, are no longer needed.
An illustrative embodiment of the present invention includes apparatus for producing and detecting radio frequencies. This illustrative embodiment includes a first unit that generates serial bus data, and a serial bus, coupled to the first unit that receives the serial bus data that is provided to it. This illustrative embodiment also includes a second unit, coupled to the serial bus, for accepting the serial bus data and creating second unit control signals, from the serial bus data. A frequency signal generating mechanism is included within the second unit. The second unit has inputs for accepting control signals and generating a frequency signal based on those control signals. The second unit also activates one of the filters and deactivates the remaining filters.